Data writing and reading method for memory device employing magnetic domain wall movement

ABSTRACT

A method of data recording and reading for a memory device employing magnetic domain wall movement. The memory device includes a writing track, an interconnecting layer formed on the writing track, and a recording track formed on the interconnecting layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No.10-2006-0089649, filed on Sep. 15, 2006, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods consistent with the present invention relate to data writing andreading of a memory device, and more particularly, to data writing andreading of a memory device employing magnetic domain wall movement.

2. Description of the Related Art

Due to developments in information technology leading to a requirementfor high capacity data storage, demand for data storage media capable ofstoring large quantities of data continues to increase. Accordingly,data storage speed has been augmented, methods of compacting storagedevices have been developed, and as a result, a wide variety of datastorage devices has been developed. A widely-used data storage medium isa hard disk drive (HDD), which includes a read/write head, and arotating medium on which data is recorded, and has the capacity forrecording 100 gigabytes (GB) of data or more. However, the rotatingparts in storage devices such as HDDs have a tendency to wear, so thatthe reliability of such devices is compromised by the likelihood of afailure during operation after a prolonged period of use.

Research and development is currently underway on a new data storagedevice that uses a magnetic domain wall movement principle.

FIGS. 1A through 1C illustrate a principle of moving a magnetic domainwall. In FIG. 1A, a magnetic wire includes a first magnetic domain 11, asecond magnetic domain 12, and a magnetic domain wall 13 between thefirst and second magnetic domains 11 and 12.

A magnetic micro region within a magnetic material will hereinafter bereferred to as a magnetic domain. In the magnetic domain, the rotationof electrons, that is, the direction of the magnetic moment of theelectrons is the same. The size and magnetization direction of such amagnetic domain can be adjusted by altering the type of magneticmaterial, its shape, and size, as well as applied external energy. Amagnetic domain wall is a partition with magnetic domains havingrespectively a variety of different magnetized magnetization directions.The magnetic domain walls may be moved through the application of amagnetic field, a current applied to a magnetic material or through acurrent.

As illustrated in FIG. 1A, after a plurality of magnetic domainsdisposed in predetermined directions are created in a magnetic layerwith a predetermined width and thickness, the magnetic domains may bemoved using magnetic fields or currents.

Referring to FIG. 1B, when a magnetic field is applied in a directionfrom the second magnetic domain 12 to the first magnetic domain 11, themagnetic domain wall 13 may move in the same direction as the directionfrom the second magnetic domain 12 to the first magnetic domain 11, thatis, in the same direction of the application of the external magneticfield. Using the same principle, when a magnetic field is applied in adirection from the first magnetic domain 11 to the second magneticdomain 12, the magnetic domain wall 13 moves in a direction from thefirst magnetic domain 11 to the second magnetic domain 12.

Referring to FIG. 1C, when an external current is supplied in thedirection from the first magnetic domain 11 to the second magneticdomain 12, the magnetic domain wall 13 moves in a direction from thesecond magnetic domain 12 to first magnetic domain 11. When a current issupplied, electrons flow in the opposite direction to the direction ofthe current, and the magnetic domain wall 13 moves in the same directionas the electrons. The magnetic domain wall moves in the directionopposite to that of the externally supplied current. When a current issupplied in the direction of the first magnetic domain wall 11 from thesecond magnetic wall 12, using the same principle, the magnetic domainwall 13 moves in a direction from the first domain 11 to the seconddomain 12.

In summary, a magnetic domain wall can be moved using an appliedexternal magnetic field or current.

The principle of moving magnetic domains may be applied to a memorydevice such as an HDD or a read only memory (ROM). Specifically, anoperation for reading/writing binary data of ‘0’ and ‘1’ is possible byusing the principle of changing the magnetic arrangement within amagnetic material by moving a magnetic domain wall of the magneticmaterial having magnetic domains magnetized in predetermined directionsand magnetic domain walls representing the boundaries there between. Aspecific current is passed through a linear magnetic material to changethe positions of the magnetic domain walls to read and write data. Thus,a highly integrated device with a simple structure may be used.Therefore, compared to conventional memories, such as ferroelectricrandom access memory (FRAM), magneto-resistive random access memory(MRAM), and phase-change random access memory (PRAM) devices, theprinciple of moving a magnetic domain wall can be applied to memorydevices with much larger storage capacities. However, applying themoving of magnetic domain walls to semiconductor devices is still in theinitial stages of development, and has a comparatively low data storagedensity. Therefore, there is a need for memory devices employingmagnetic domain wall movement with structures optimized for high-densitydevices.

SUMMARY OF THE INVENTION

The present invention provides a method of data recording in a memorydevice employing magnetic domain wall movement.

The present invention also provides a method of reading data written ina memory device employing magnetic domain wall movement.

According to an aspect of the present invention, there is provided amethod of recording data in a memory device including a writing track,an interconnecting layer formed on the writing track, and a datarecording track formed on the interconnecting layer, and employingmovement of a magnetic domain wall, the method including: positioning afirst magnetic domain with a spin direction to write data on the writingtrack contacting the interconnecting layer; magnetizing theinterconnecting layer contacting the writing track to have a same spindirection as the first magnetic domain; and forming a second magneticdomain having the same spin direction as the first magnetic domain onthe data recording track contacting the interconnecting layer.

The positioning of the first magnetic domain may include moving thefirst magnetic domain to an area contacting the interconnecting layer,through applying a current through both ends of the writing track.

The forming of the second magnetic domain may include applying a currentin a direction from the data recording track to the writing track, andforming the second magnetic domain on the data recording track.

The writing track and the data recording track may be formed of amagnetic material having a magnetic anisotropy constant value of between10⁵ J/m³ and 10⁷ J/m³.

The writing track and the data recording track may be formed with amaterial including at least one of CoPt and FePt.

The interconnecting layer may be formed of a magnetic material having amagnetic anisotropy constant between 10² and 10³ J/m³.

The interconnecting layer may be formed of at least one of NiFe, CoFe,Ni, Fe, Co, and an alloy including at least one thereof.

According to another aspect of the present invention, there is provideda method of reading data in a memory device including a writing trackwith a magnetic resistance sensor, an interconnecting layer formed on afirst end of the writing track, and a data recording track formed on theinterconnecting layer, and employing a movement of a magnetic domainwall, the method including: moving magnetic domains of the writing trackwith mutually different magnetized directions towards a second end ofthe writing track; moving magnetic domains of the data recording trackthrough the interconnecting layer toward the writing track; anddetecting magnetized directions of the magnetic domains moved from thedata recording track to the writing track through the magneticresistance sensor.

The magnetic domains of the writing track may be moved through applyinga current through the first end and the second end of the writing track.

The magnetic domains of the data recording track may be moved byapplying a current through the data recording track and the magneticresistance sensor.

The detecting of the magnetized directions may include applying avoltage to the data recording track and the writing track after magneticdomains are moved from the data recording track to the writing track,and contacting the magnetic domains moved to the writing track with themagnetic resistance device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent and more readily appreciated from the following detaileddescription of certain exemplary embodiments of the invention, taken inconjunction with the accompanying drawings of which:

FIGS. 1A through 1C are perspective views illustrating a movingprinciple of a magnetic domain wall;

FIG. 2 is a perspective view of a memory device employing magneticdomain wall movement, according to an exemplary embodiment of thepresent invention;

FIGS. 3A through 3H are perspective illustrating a method of writingdata in a memory device employing a magnetic domain wall movement,according to an exemplary embodiment of the present invention; and

FIGS. 4A through 4L are perspective views illustrating a method ofreading data in a memory device employing magnetic domain wall movementaccording to exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The method of writing and reading data in a memory device employing amagnetic domain wall movement according to the present invention willnow be described more fully with reference to the accompanying drawings,in which exemplary embodiments of the invention are shown. In thedrawings, the thicknesses and widths of layers are exaggerated forclarity.

FIG. 2 is a perspective view of a memory device employing magneticdomain wall movement, according to an exemplary embodiment of thepresent invention.

Referring to FIG. 2, a memory device, including a recording track 21formed in a first direction, a writing track 23 formed in a seconddirection, and a soft magnetic interconnecting layer 22 formed betweenthe recording track 21 and the writing track 23, is provided.

The recording track 21 and the writing track 23 are formed usingmaterial having high magnetic anisotropy characteristics to achieveincreased data recording density. When a material having a magneticanisotropy constant of 10⁵ J/m³ or more is required, a high Ku materialhaving a magnetic anisotropy energy constant of 10⁵ J/m³ to 10⁷ J/m³ maybe used. Specific examples of such a materials are CoPt, FePt, andalloys thereof, which have perpendicular magnetization characteristics.The recording track 21 and writing track 23 may be formed in singlelayer or multi layer structures. The thickness of each of the recordingtrack 21 and the writing track 23 may be 1 to 100 nm.

The interconnecting layer 22 is formed with a low Ku material with amagnetic anisotropy characteristic that is lower than those of therecording track 21 and writing track 23. When the interconnecting layer22 is to be formed of a material with a magnetic anisotropy constantlower than 10³ J/m³ a material having a magnetic anisotropy constant ofbetween 10² to 10³ J/m³ may be used. Specific examples of such materialsare NiFe, CoFe, Ni, Fe, Co, and alloys including at least one of thematerials. When the thickness of the interconnecting layer 22 isrequired to be formed to 10 nm or more, it may be between 10 to 100 nm.The interconnecting layer 22 may be formed in a single or multi layerstructure.

While the recording track 21 and writing track 23 in FIG. 2 areillustrated as being parallel with each other, they may be configured invarious ways according to the conditions of use. For example, therecording track 21 and writing track 23 may be formed to cross or to beorthogonal to each other. Furthermore, the recording track 21 andwriting track 23 may be formed in a wire configuration with a pluralityof magnetic domains.

A data writing method of a memory device employing magnetic domain wallmovement illustrated in FIG. 2 will be described in detail below, withreference to FIGS. 3A through 3H.

Referring to FIG. 3A, a recording track 31 and a writing track 33 areformed having an interconnecting layer 32 formed there between.Connected to one end of the recording track 31 is a first conductingwire E1 formed of a conductive material, a second conductive wire E2 isformed connected to one end of the writing track 33, and a thirdconductive wire E3 is formed connected to the other end of the writingtrack 33. A magnetic domain region A1 having an magnetization directionpointing upward and a magnetic domain region A2 having a magnetizationdirection pointing downward are formed on the writing track 33. In thecase of the recording track 31, the magnetization is arbitrarily shownin the upward direction. A magnetization in a downward direction is setas “0”, and magnetization in an upward direction is set as “1”. Adescription of recording data as “0” on the data recording track 31 whenthe magnetization is in a downward direction will be described below.

Referring to FIG. 3B, the second conductive wire E2 and the thirdconductive wire E3 are both set to an ON state and also a current issupplied through the second conductive wire E2 and the third conductivewire E3, which are connected on either end of the writing track 33.

Referring to FIG. 3C, when a current is made to flow from the secondconductive wire E2 towards the third conductive wire E3, a magneticdomain wall moves in the direction opposite to the flow of current. Themagnetic domain wall moves in the direction of the movement ofelectrons, so that it moves in a direction opposite to the direction ofthe current. Accordingly, the magnetic domain wall moves toward thesecond conductive wire E2. As a result, the length of the magneticdomain A1 of the writing track 33 is reduced, and the length of themagnetic domain A2 is increased. When the magnetic domain A2 ispositioned below the interconnecting layer 32, the interconnecting layer32 is affected by the magnetic domain A2 and is magnetized in the samedirection as the magnetic domain A2.

Referring to FIG. 3D, the second conductive wire E2 at the left end ofthe writing track 33 is set in an OFF state, and the first conductivewire E1 on the left end of the data recording track 31 is set in an ONstate. Also, a current is made to flow through the first and thirdconductive wires E1 and E3. The direction of current flow is set fromthe first conductive wire E1 to the third conductive wire E3, themagnetic domain A2 with a downward magnetization expands towards thedata recording track 31 through the interconnecting layer 32, and themagnetization in a downward direction in the magnetic domain A3 expandstowards the left end of the data recording track 31, and as such data“0” is recorded.

Referring to FIG. 3E, in order to expand the magnetic domain A3 towardthe left side of the data recording track 31, a current is made to flowfrom the first conductive wire E1 towards the third conductive wire E3.

Next, after the data “0” is recorded on the data recording track 31, aprocess of recording a magnetic domain region with an upwardmagnetization, that is, with data “1” on the data recording track 31will be described.

Referring to FIG. 3F, the first conductive wire E1 is set in an OFFstate, and the second conductive wire E2 and the third conductive wireE3 are set in an ON state, and current is supplied.

Referring to FIG. 3G, current is made to flow from the third conductivewire E3 toward the second conductive wire E2. When current flows fromthe third conductive wire E3 toward the second conductive wire E2,electrons move from the second conductive wire E2 towards the thirdconductive wire E3. Accordingly, the magnetic domain wall, that is abarrier between the magnetic domain A1 with an upward magnetization andthe magnetic domain A2 with a downward magnetization, moves in adirection to the right of the writing track 33 towards the thirdconductive wire E3. Current is supplied until the magnetic domain wallbetween the magnetic domain A1 and the magnetic domain A2 passes througha region corresponding to the interconnecting layer 32. The magneticdomain A1 contacts the interconnecting layer 32, so that theinterconnecting layer 32 adopts a magnetization in the same upwarddirection as the magnetic domain A1 of the writing track 33.

Referring to FIG. 3H, the first conductive wire E1 and the secondconductive wire E2 are set in an ON state, and the third conductive wireE3 is set in an OFF state. When a current is supplied from the firstconductive wire E1 towards the second conductive wire E2, electrons movefrom the second conductive wire E2 towards the first conductive wire E1.Accordingly, a magnetic domain A4 that is magnetized in an upwarddirection passes through the interconnecting layer 32 and expands in thedata recording track 31. As a resultant, the downward magnetizationdirection of the portion of the data recording track 31 directly abovethe interconnecting layer 32 changes to the upward magnetizationdirection of the magnetic domain A4. Thus, a data region “1” is createdto the right of the data region “0”.

A detailed description of a data reading and writing method in a memorydevice employing magnetic domain wall movement as illustrated in FIG. 2will be given below, with reference to FIGS. 4A through 4L.

Referring to FIG. 4A, recording track 41 and a writing track 43 areformed having an interconnecting layer 42 formed there between. Theinterconnecting layer 42 may be formed as a single layer or a multilayer. A first conductive wire E1 formed of a conductive material isformed connected to the left end of the recording track 41, a secondconductive wire E2 is formed connected to one end of the writing track43, and a third conductive wire E3 is formed connected to the other endof the writing track 43A magneto-resistance sensor 44 for reading amagnetized direction of a magnetic domain in a predetermined location ofthe writing track 43 contacts the central region of the writing track43. An electrode S1 for measuring a resistance state of themagneto-resistance sensor 44 is formed on the magnetic resistance sensor44, and a fourth conductive wire E4 and a fifth conductive wire E5 forapplying a current to the writing track 43 are formed on either side ofthe magnetic resistance sensor 44. The magneto-resistance sensor 44 maybe a conventional giant magneto-resistance (GMR) sensor or a tunnelingmagneto-resistance (TMR) sensor that are capable of detecting theresistance direction in a recording medium.

Referring to FIG. 4B, the writing track 43 must have two magneticdomains magnetized in mutually opposite directions in order to recorddata on the data recording track 41. Accordingly, in order to preservethe magnetic domains of the magnetic domain B1 magnetized in an upwarddirection and the magnetic domain magnetized oppositely to B1 in adownward direction, the first conductive wire E1 must first be set in anOFF state, and the second and third conductive wires E2 and E3 must beset in ON states. Also, current is made to flow from the thirdconductive wire E3 towards the second conductive wire E2. Thus,electrons move from the second conductive wire E2 towards the thirdconductive wire E3, and the area of the magnetic domain B1 expandstowards the third conductive wire E3. Current is supplied until themagnetic domain B1 passes the region contacting the magneto-resistancesensor 44.

Referring to FIG. 4C, the first conductive wire E1 and the sensorelectrode are set in an ON state, and the second conductive wire E2 andthe third conductive wire E3 are set in an OFF state.

Referring to FIGS. 4C and 4D, current is supplied from the fourthconductive wire E4 towards the first conductive wire E1. Electrons movefrom the first conductive wire E1 towards the fourth conductive wire E4,so that the magnetic domain B2 and the magnetic domain B3 pass throughthe interconnecting layer 42 and move toward the writing track 43. Themagnetic domain B2 is magnetized in the same direction as the magneticdomain B1, and combines with the magnetic domain B1.

Referring to FIG. 4E, current is continuously supplied from the fourthconductive wire E4 towards the first conductive wire E1. Thus, themagnetic domains of the recording track 41 continuously move toward thewriting track 43. By making current flow from the fourth conductive wireE4 towards the first conductive wire E1, the magnetic domain B1 of thewriting track 43 does not move toward the third conductive wire E3, andthe magnetic domain B3 and the magnetic domain B4 move from therecording track 41 so that the areas thereof gradually shrinks. As aresult, current is supplied through the first conductive wire E1 and thefourth conductive wire E4 until the magnetic domains B5 and B6 movetoward the writing track 43, as illustrated in FIGS. 4F and 4G.

Referring to FIG. 4H, the first conductive wire E1 and the thirdconductive wire E3 are set in an ON state, and current is supplied fromthe third conductive wire E3 towards the first conductive wire E1. Theelectrons move from the first conductive wire E1 towards the thirdconductive wire E3, so that the magnetic wall moves in the samedirection.

Referring to FIG. 4I, all the tracks of the data recording track 41 andthe writing track 43, for example, magnetic domains B1, B3, B4, B5, andB6 move toward the third conductive wire E3 that is the right end of thewriting track 43. When the magnetic domains pass the magneto-resistancesensor 44 contacting the writing track 43, the magneto-resistance sensor44 reads the resistance directions of the magnetic domains to read thedata recorded on the magnetic domains.

When all the data required is read, the magnetic domains of the writingtrack 43 are moved to the original positions on the recording track 41to complete the reading operation.

Referring to FIGS. 4J through 4L, the first conductive wire E1 and thethird conductive wire E3 are set in an ON state. A current is suppliedfrom the first conductive wire E1 towards the third conductive wire E3.Here, the electrons move from the third conductive wire E3 towards thefirst conductive wire E1, so that the magnetic domain wall moves in thesame as the electron flow. The movement of the magnetic domain wallcauses the magnetic domains B6, B5, B4, and B3 located on the writingtrack 43 to pass the interconnecting layer 42 and move towards the datarecording track 41. Resultantly, a current is supplied through the firstconductive wire E1 and the third conductive wire E3 until the magneticdomain B1 is positioned on the left end of the writing track 43, so thatthe magnetic domains move back to their original positions, completingthe reading operation.

The present invention includes the following advantages.

First, when operating a memory device, unlike in an HDD, themagneto-resistance sensor and the data recording medium are notmechanically moved, and allow the recording and reading of data.Therefore, mechanical wear does not occur, extending the lifespan of theproduct, and providing outstanding reliability.

Second, the size of the memory device may be miniaturized, and thewriting and reading of data is simplified, so that the device isappropriate for application in mobile devices. Also, due to its abilityto be miniaturized, the memory device may be made into a high-densitydevice capable of storing data having a density of terabits/in².

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims. Forexample, in the memory device according to the present invention, themagnetic resistance sensor may be disposed above the data recordingtrack contacting a soft magnetic interconnecting layer, and not disposedbelow the writing track, and the fourth conductive wire may be formed ina predetermined location below the writing track. Therefore, the scopeof the invention is defined not by the detailed description of theinvention but by the appended claims, and all differences within thescope will be construed as being included in the present invention.

1. A method of recording data in a memory device comprising a writingtrack, an interconnecting layer disposed on the writing track, and arecording track disposed on the interconnecting layer, and employingmovement of a magnetic domain wall, the method comprising: positioning afirst magnetic domain having a magnetization direction to write data ona portion of the writing track contacting the interconnecting layer;magnetizing the interconnecting layer contacting the writing track tohave a magnetization direction which is the same as the magnetizationdirection of the first magnetic domain; and forming a second magneticdomain having a magnetization direction which is the same as themagnetization direction of the first magnetic domain on a portion of thedata recording track contacting the interconnecting layer.
 2. The methodof claim 1, wherein the writing track comprises the first magneticdomain and a third magnetic domain having a magnetization directionwhich is opposite to the magnetization direction of the first magneticdomain.
 3. The method of claim 2, wherein the positioning of the firstmagnetic domain comprises moving the first magnetic domain to an areacontacting the interconnecting layer, by making a current flow throughboth ends of the writing track.
 4. The method of claim 1, wherein theforming of the second magnetic domain comprises making a current flow ina direction from the data recording track to the writing track, andforming the second magnetic domain on the data recording track.
 5. Themethod of claim 1, wherein the writing track and the data recordingtrack comprises a magnetic material having a magnetic anisotropyconstant of between 10⁵ J/m³ and 10⁷ J/m³.
 6. The method of claim 5,wherein the writing track and the data recording track comprise at leastone of CoPt and FePt.
 7. The method of claim 1, wherein theinterconnecting layer comprises a magnetic material having a magneticanisotropy constant of between 10² and 10³ J/m³.
 8. The method of claim7, wherein the interconnecting layer comprises at least one of NiFe,CoFe, Ni, Fe, Co, and an alloy comprising at least one NiFe, CoFe, Ni,Fe and Co.
 9. A method of reading data in a memory device comprising awriting track having a magneto-resistance sensor, an interconnectinglayer disposed on a first end of the writing track, and a data recordingtrack disposed on the interconnecting layer, and employing a movement ofa magnetic domain wall, the method comprising: moving magnetic domainsof the writing track with mutually different magnetization directionstoward a second end of the writing track; moving magnetic domains of thedata recording track through the interconnecting layer toward thewriting track; and detecting magnetization directions of the magneticdomains moved from the data recording track to the writing track usingthe magneto-resistance sensor.
 10. The method of claim 9, wherein themagnetic domains of the writing track are moved by making a current flowthrough the first end and the second end of the writing track.
 11. Themethod of claim 9, wherein the magnetic domains of the data recordingtrack are moved by making a current flow through the data recordingtrack and an electrode which is disposed beside the magnetic resistancesensor.
 12. The method of claim 9, wherein the detecting of themagnetization directions comprises applying a voltage to the datarecording track and the writing track after magnetic domains are movedfrom the data recording track to the writing track, and contacting themagnetic domains moved to the writing track with the magnetic resistancesensor.
 13. The method of claim 9, wherein the writing track and thedata recording track comprise a magnetic material having a magneticanisotropy constant of between 10⁵ J/m³ and 10⁷ J/m³.
 14. The method ofclaim 9, wherein the writing track and the data recording track compriseat least one of CoPt and FePt.
 15. The method of claim 9, wherein theinterconnecting layer comprises a magnetic material having a magneticanisotropy constant of between 10² and 10³ J/m³.
 16. The method of claim15, wherein the interconnecting layer comprises at least one of NiFe,CoFe, Ni, Fe, Co, and an alloy comprising at least one NiFe, CoFe, Ni,Fe and Co.